1720687661 has 16 divisors (see below), whose sum is σ = 2238547968. Its totient is φ = 1282498800.

The previous prime is 1720687649. The next prime is 1720687663. The reversal of 1720687661 is 1667860271.

It is not a de Polignac number, because 1720687661 - 2²² = 1716493357 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1720687663) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 484025 + ... + 487566.

It is an arithmetic number, because the mean of its divisors is an integer number (139909248).

Almost surely, 2^1720687661 is an apocalyptic number.

1720687661 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

1720687661 is a deficient number, since it is larger than the sum of its proper divisors (517860307).

1720687661 is a wasteful number, since it uses less digits than its factorization.

1720687661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 971632.

The product of its (nonzero) digits is 169344, while the sum is 44.

The square root of 1720687661 is about 41481.1723677140. The cubic root of 1720687661 is about 1198.3049356934.

The spelling of 1720687661 in words is "one billion, seven hundred twenty million, six hundred eighty-seven thousand, six hundred sixty-one".